1. Field of the Invention
This disclosure relates in general to magnetic storage systems, and more particularly to a method and apparatus for defining leading edge taper of a write pole tip.
2. Description of Related Art
There has been huge progress in the field of magnetic storage system technology in almost 50 years. Moreover, the rate of this progress is increasing year after year. Such success has made storage systems an important component of modern computers.
Some of the most important customer attributes of any storage system are the cost per megabyte, data rate, and access time. In order to obtain the relatively low cost of today's storage system compared to solid state memory, the customer must accept the less desirable features of this technology, which include a relatively slow response, high power consumption, noise, and the poorer reliability attributes associated with any mechanical system. On the other hand, magnetic storage systems have always been nonvolatile; i.e., no power is required to preserve the data, an attribute which in semiconductor devices often requires compromises in processing complexity, power-supply requirements, writing data rate, or cost.
Improvements in areal density have been the chief driving force behind the historic improvement in storage cost. In fact, the areal density of magnetic storage systems continues to increase. While nature allows us to scale down the size of each bit of information, it does not allow scaling to happen forever.
Today, as the magnetic particles that make up recorded data on a storage system become ever smaller, technical difficulties in writing and reading such small bits occur. Further, as areal density increases, the requirements put on head designs will change.
In a magnetic head, a read element and a write element are formed having an air bearing surface ABS, in a plane, which can be aligned to face the surface of the magnetic disk. The read element includes a first shield, a second shield, and a read sensor that is located within a dielectric medium between the first shield and the second shield. The most common type of read sensor 48 used in the read/write head 28 is the magnetoresistive (AMR or GMR) sensor, which is used to detect magnetic field signal changes in a magnetic medium by means of changes in the resistance of the read sensor imparted from the changing magnitude and direction of the magnetic field being sensed.
The write element is typically an inductive write element that includes the second shield that functions as a first pole for the write element and a second pole disposed above the first pole. The first pole and the second pole contact one another at a backgap portion, with these three elements collectively forming the yoke. The combination of a first pole tip portion and a second pole tip portion near the ABS are sometimes referred to as the ABS end 56 of the write element. Some write elements have included a pedestal that can be used to help define track width and throat height. A write gap is formed between the first and second poles in the area opposite the back gap portion. The write gap is typically filled with a non-magnetic, electrically insulating material that forms a write gap material layer. A conductive coil passes through the yoke. The write head operates by passing a write current through the conductive coil. Because of the magnetic properties of the yoke, a magnetic flux is induced in the first and second poles by write currents passed through the coil. The write gap allows the magnetic flux to fringe out from the yoke thus forming a fringing gap field and to cross the magnetic recording medium that is placed near the ABS.
As the demand for storage has increased dramatically over time, technologists have worked toward increasing the amount of information that can be stored onto disc drives. By increasing the areal density—or the amount of information that can be placed within a given area on a disc drive—technologists in fact have been able to deliver densities in excess of 100 percent annually over the course of the last several years. A key end-result or benefit of this dramatic areal density curve is that disc drive manufacturers have also been able to drive down the cost of the disc drives themselves because they can offer higher capacity disc drives using fewer platters, heads, and mechanical parts.
For the past 40 years, longitudinal recording has been used to record information on a disc drive. In longitudinal recording, the magnetization in the bits on a disc is flipped between lying parallel and anti-parallel to the direction in which the head is moving relative to the disc.
However, increasing areal densities to allow greater capacities is no small task. Today it is becoming more challenging to increase areal densities in longitudinal recording. To go to even higher areal densities, researchers are looking at several alternatives, including perpendicular recording.
In recent years, the increased demand for higher data rate and areal density has correspondingly fueled the perpendicular head design to scale toward smaller dimensions and the need for constant exploration of new head designs, materials, and practical fabrication methods. A robust head design must consider the challenges in forming a beveled write pole, placement of the flare point and edge of the leading edge tapering (LET), and aggressive alignments and throat heights of the critical layers in the head design to achieve optimal effective write field and field gradient while minimizing adjacent track issues (ATI).
The write pole (P3) is the critical structure in the head design that needs to be optimized to bring maximal effective write field to the pole tip. One approach is to “bring” the flare point of P3 and the flux guide layer (P2) closer to the air bearing surface (ABS) to achieve higher write field. However, this has proven to be challenging because the ability to simultaneously control both flare point and track-width using ion milling approach is difficult due to the physical nature of this destructive method.
Equally challenging in “bringing” the flux guide layer closer to the ABS is ATI issues. The P2 structure is much bigger in area at the ABS view as compared to the write pole. A write field that is generated by an applied current would prefer to leak from P2 instead of being funneled toward the pole tip. When P2 is brought closer to the ABS, it will contribute significantly to ATI such as side writing and side erasure. One promising approach is to introduce leading edge tapering (LET) to the pole tip. This method would essential bring a more effective write field to the P3 pole tip and relax the stringent requirement to bring the flare point and P2 shaping layer closer to the ABS to achieve higher write field.
The effectiveness of tapering is achieved when it is self-aligned to P3 and the tapering angle is optimized at forty-five degree or more. Controlled methods using ion mill approach to fabricate LET in the past have proven to be of great difficulty to simultaneously achieve both optimal LET angle, tight placement of the LET's edge and couple this process into P3 fabrication to define LET's width at the ABS to minimize ATI issues.
It can be seen then that there is a need for a method and apparatus for defining leading edge taper of a write pole tip.